Rhiwallon being the most able practitioner became the eminent personal physician to Lord Rhys at Dinefwr. Rhiwallon was assisted by his three sons, Cadwgan, Griffith and Einon. In return, they were rewarded with land around Myddfai.
“Lord Rhys maintained their rights and privileges in all integrity and honour was met.”
It is at these monasteries that the Physicians would have acquired a lot of their practical skills of herbal medicine. The scholasticism of the monks too would have encouraged writing their recipes down. This they did, “As a record of their skill lest no one should be found with the skill they were.” However, as Pughe states, “it is unlikely that their materia medica came from that era.” Most likely it was an accumulation of knowledge from the preceding centuries of herbal usage by the tribes and villages of South Wales.